EP0641802A2 - Process for treating cellulose - Google Patents

Process for treating cellulose Download PDF

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Publication number
EP0641802A2
EP0641802A2 EP94111025A EP94111025A EP0641802A2 EP 0641802 A2 EP0641802 A2 EP 0641802A2 EP 94111025 A EP94111025 A EP 94111025A EP 94111025 A EP94111025 A EP 94111025A EP 0641802 A2 EP0641802 A2 EP 0641802A2
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EP
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Prior art keywords
ammonia
cellulose
pressure
pulp
mass
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EP94111025A
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German (de)
French (fr)
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EP0641802A3 (en
EP0641802B1 (en
Inventor
Karl Prof. Dr. Bredereck
Ties Dr. Karstens
Harro Prof. Dr. Lentz
Hans Dr. Steinmeier
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Cerdia Produktions GmbH
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Rhone Poulenc Rhodia AG
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B1/00—Preparatory treatment of cellulose for making derivatives thereof, e.g. pre-treatment, pre-soaking, activation
    • C08B1/02—Rendering cellulose suitable for esterification
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B1/00—Preparatory treatment of cellulose for making derivatives thereof, e.g. pre-treatment, pre-soaking, activation

Definitions

  • the invention relates to a process for the treatment of cellulose for its activation for subsequent chemical reactions by contacting the cellulose with liquid ammonia at a pressure which is higher than atmospheric pressure in a pressure vessel and subsequent relaxation by rapidly reducing the pressure to atmospheric pressure.
  • the activation is usually carried out by treating the pulp with acetic acid (cf. Ullmann's Encyclopedia of Industrial Chemistry, Fifth, Completely Revised Edition, Volume A 5, page 440 - VCH Verlagsgesellschaft mbH, D-6940 Weinheim, Federal Republic of Germany 1986) .
  • acetic acid cf. Ullmann's Encyclopedia of Industrial Chemistry, Fifth, Completely Revised Edition, Volume A 5, page 440 - VCH Verlagsgesellschaft mbH, D-6940 Weinheim, Federal Republic of Germany 1986.
  • this known activation process may result in no homogeneous activation of the cellulose, since the crystalline regions of this cellulose are difficult to access for the pure acetic acid (glacial acetic acid) used. This then means that in the subsequent acetylation the desired cellulose triacetate stage is reached earlier in the amorphous areas of the pulp than in the crystalline areas.
  • the method according to European patent application 0 077 287 is not suitable for the activation of pulp which is subsequently to be acetylated, in that the ammonia remaining in the pulp after relaxation reacts with the acetylating agent acetic acid and the acetylating catalyst sulfuric acid with the formation of salts; as a result, the ammonia remains - in bound form - in the acetylation and in the subsequent saponification process and finally, after the precipitation of the cellulose acetate, reaches the waste water, which is highly undesirable.
  • the invention is therefore based on the object of providing a process for the treatment of cellulose, in particular pulp, for its activation for subsequent chemical reactions, in particular for the subsequent acetylation, with the aid of liquid ammonia
  • cellulose in particular pulp
  • the invention is also intended to achieve a high-level and at the same time homogeneous activation, particularly with regard to subsequent acylation reactions.
  • the quantitative ratio of ammonia to pulp is 6 mass units of ammonia to 10 mass units of pulp to 10 mass units of ammonia to 10 mass units of pulp.
  • the content of residual ammonia still necessary for maintaining the activation state is 2 to 4% by mass of ammonia, based on the mass of pulp.
  • water, water vapor, superheated water vapor, an ether, an epoxy, a glycol, a hydrocarbon, an inert gas or carbon dioxide be used as another swelling or inclusion agent.
  • gaseous ammonia escaping during the expansion is collected and compressed again to liquid ammonia.
  • a pressure vessel ie a pressure-resistant vessel, is used for the method according to the invention.
  • the term “pressure vessel” is to be understood as far as possible within the meaning of the invention.
  • the pressure vessel can be, for example, an autoclave or an extruder for the process to be carried out continuously.
  • the device for quasi-continuous technical-chemical processes in compressed fluids described in the - as yet unpublished - German patent application P 42 16 295.5 can also be used as a pressure vessel for the method according to the invention.
  • the ammonia is expanded by rapidly reducing the pressure to atmospheric pressure. This means that the pressure should be reduced to atmospheric pressure as suddenly as possible, preferably within a period of a few seconds, very particularly preferably within a period of less than 1 Second.
  • the pulp is introduced into a pressure vessel, such as an autoclave, and liquid ammonia under pressure is applied to it.
  • the temperature in the pressure vessel is usually the temperature of the environment, ie room temperature; however, the use of temperatures higher than room temperature is also possible, which is advantageous in that the subsequent removal of the ammonia from the pressure vessel is facilitated during the relaxation.
  • a cylindrical autoclave made of V 4 A steel with a capacity of 750 ml was used for the method according to the invention.
  • 50 g of mechanically pulped pulp were placed in this autoclave brought in.
  • the cellulose used had an ⁇ -cellulose content of 96% by mass.
  • 50 g of liquid ammonia were introduced into the now closed autoclave through a valve at the top of the autoclave, after which the valve was closed.
  • the temperature in the autoclave was 20 ° C. After introduction of the ammonia and at the aforementioned temperature of 20 ° C, the pressure in the autoclave was 6 bar.
  • the duration of exposure of the ammonia to the pulp was 30 minutes.
  • the aforementioned valve on the autoclave was opened, as a result of which the ammonia escaped suddenly and the contents of the autoclave were released to atmospheric pressure.
  • the autoclave - with the valve open - was heated in a water bath at a temperature of 40 ° C. for a period of 15 minutes.
  • the desired minimum ammonia content of 4% by mass was checked gravimetrically.
  • steam was introduced into the autoclave through the aforementioned valve on the autoclave until a pressure of 4 bar was reached, after which the valve was closed again.
  • the water vapor had a temperature of 145 ° C.
  • the duration of exposure to water vapor to the pulp was 5 minutes.
  • the pressure was then released again to atmospheric pressure by opening the valve mentioned several times.
  • the pulp was then removed from the autoclave and acetylated to determine the reactivity. It was found that the acetylation period of this pulp up to the cellulose triacetate stage was reduced by 50% compared to that of a pulp which had been activated with glacial acetic acid: the acetylation period for the cellulose activated according to this example was only 20 minutes, whereas that Acetylation time for a pulp that was activated with glacial acetic acid was 40 minutes.

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Biochemistry (AREA)
  • Materials Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Polysaccharides And Polysaccharide Derivatives (AREA)
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Abstract

Beschrieben wird ein Verfahren zur Behandlung von Cellulose zu deren Aktivierung für nachfolgende chemische Reaktionen durch Inkontaktbringen der Cellulose mit flüssigem Ammoniak bei gegenüber Atmosphärendruck erhöhtem Druck in einem Druckgefäß und anschließende Entspannung durch rasche Reduzierung des Drucks auf Atmosphärendruck, wobei

  • als Cellulose Zellstoff mit einem Gehalt an α-Cellulose von mindestens 92 Masse-% eingesetzt wird,
  • man das Ammoniak bei Raumtemperatur oder bei einer höheren Temperatur als Raumtemperatur auf den Zellstoff einwirken läßt,
  • man nach der Entspannung das im Druckgefäß dann noch verbliebene Ammoniak bis auf einen Minimalgehalt, bei dem der durch die Einwirkung des Ammoniaks erreichte Aktivierungszustand noch erhalten bleibt, entfernt
    und
  • man schließlich das für die Aufrechterhaltung des Aktivierungszustands noch notwendige restliche Ammoniak durch ein anderes Quell- oder Inklusionsmittel ersetzt.
A method is described for the treatment of cellulose for its activation for subsequent chemical reactions by contacting the cellulose with liquid ammonia at a pressure which is higher than atmospheric pressure in a pressure vessel and subsequent relaxation by rapidly reducing the pressure to atmospheric pressure, wherein
  • cellulose with a content of α-cellulose of at least 92% by mass is used,
  • the ammonia is allowed to act on the pulp at room temperature or at a temperature higher than room temperature,
  • after the expansion, the ammonia still remaining in the pressure vessel is removed to a minimum content at which the activation state achieved by the action of the ammonia is still retained
    and
  • finally, the remaining ammonia necessary for maintaining the activation state is replaced by another swelling or inclusion agent.

Description

Die Erfindung betrifft ein Verfahren zur Behandlung von Cellulose zu deren Aktivierung für nachfolgende chemische Reaktionen durch Inkontaktbringen der Cellulose mit flüssigem Ammoniak bei gegenüber Atmosphärendruck erhöhtem Druck in einem Druckgefäß und anschließende Entspannung durch rasche Reduzierung des Drucks auf Atmosphärendruck.The invention relates to a process for the treatment of cellulose for its activation for subsequent chemical reactions by contacting the cellulose with liquid ammonia at a pressure which is higher than atmospheric pressure in a pressure vessel and subsequent relaxation by rapidly reducing the pressure to atmospheric pressure.

Cellulose, insbesondere Zellstoff, die/der acetyliert werden soll, muß vor der Acetylierung aktiviert werden. Üblicherweise erfolgt die Aktivierung dadurch, daß der Zellstoff mit Essigsäure behandelt wird (vergleiche dazu Ullmann's Encyclopedia of Industrial Chemistry, Fifth, Completely Revised Edition, Volume A 5, Seite 440 - VCH Verlagsgesellschaft mbH, D-6940 Weinheim, Federal Republic of Germany 1986). Je nach Verfahrensbedingungen kann es bei diesem bekannten Aktivierungsverfahren vorkommen, daß keine homogene Aktivierung des Zellstoffs erfolgt, da die kristallinen Bereiche dieses Zellstoffs für die eingesetzte reine Essigsäure (Eisessig) schlecht zugänglich sind. Dieses führt dann dazu, daß bei der nachfolgenden Acetylierung die angestrebte Cellulosetriacetat-Stufe in den amorphen Bereichen des Zellstoffs früher erreicht wird als in den kristallinen Bereichen.Cellulose, especially pulp to be acetylated, must be activated before acetylation. The activation is usually carried out by treating the pulp with acetic acid (cf. Ullmann's Encyclopedia of Industrial Chemistry, Fifth, Completely Revised Edition, Volume A 5, page 440 - VCH Verlagsgesellschaft mbH, D-6940 Weinheim, Federal Republic of Germany 1986) . Depending on the process conditions, this known activation process may result in no homogeneous activation of the cellulose, since the crystalline regions of this cellulose are difficult to access for the pure acetic acid (glacial acetic acid) used. This then means that in the subsequent acetylation the desired cellulose triacetate stage is reached earlier in the amorphous areas of the pulp than in the crystalline areas.

Aus der Zeitschrift "Acta Polymerica" 32 (1981), Heft 3, Seiten 164 bis 171, ist es bekannt, flüssiges Ammoniak für die Aktivierung von Cellulose einzusetzen, und zwar bei Normaldruck und bei einer Temperatur von - 50 bis - 60 °C. Die Anwendung von flüssigem Ammoniak zur Aktivierung von Cellulose bietet gegenüber Eisessig den Vorteil, daß auch die kristallinen Bereiche der Cellulose - durch die Aufweitung des Kristallgitters - besser zugänglich werden. Die technische Anwendung dieses Verfahrens ist, bedingt durch die tiefe Temperatur, jedoch ziemlich aufwendig, was eine mögliche Erklärung dafür ist, daß dieses Verfahren nicht produktionsmäßig angewandt wird.From the magazine "Acta Polymerica" 32 (1981), volume 3, pages 164 to 171, it is known to use liquid ammonia for the activation of cellulose, at normal pressure and at a temperature of - 50 to - 60 ° C. The use of liquid ammonia to activate cellulose has the advantage over glacial acetic acid that the crystalline areas of cellulose are more accessible due to the expansion of the crystal lattice. However, due to the low temperature, the technical application of this method is rather complex, which is a possible explanation for the fact that this method is not used in production.

Ferner ist aus der europäischen Patentanmeldung 0 077 287 die Anwendung von flüssigem Ammoniak für die Aktivierung von in Futtermitteln enthaltener Cellulose unter Anwendung von erhöhtem Druck bekannt. Nach dem Verfahren gemäß der europäischen Patentanmeldung 0 077 287 wird das Cellulose enthaltende Material bei hohem Druck mit flüssigem Ammoniak behandelt, wonach eine rasche Reduzierung des Drucks auf Atmosphärendruck erfolgt, wodurch das Ammoniak siedet und die Cellulose aufgefasert wird.
Das Verfahren gemäß der europäischen Patentanmeldung 0 077 287 ist zur Aktivierung von Zellstoff, der anschließend acetyliert werden soll, insofern nicht geeignet, als das nach der Entspannung im Zellstoff noch verbleibende Ammoniak mit dem Acetylierungsmittel Essigsäure und dem Acetylierungs-Katalysator Schwefelsäure unter Salzbildung reagiert; dadurch verbleibt das Ammoniak - in gebundener Form - im Acetylierungs- und im nachfolgenden Verseifungsprozeß und gelangt schließlich so, nach der Fällung des Celluloseacetats, in das Abwasser, was in hohem Maße unerwünscht ist.Furthermore, from European patent application 0 077 287 the use of liquid ammonia for the activation of cellulose contained in animal feed using increased pressure is known. According to the process according to European patent application 0 077 287, the cellulose-containing material is treated at high pressure with liquid ammonia, after which the pressure is rapidly reduced to atmospheric pressure, causing the ammonia to boil and the cellulose to be fiberized.
The method according to European patent application 0 077 287 is not suitable for the activation of pulp which is subsequently to be acetylated, in that the ammonia remaining in the pulp after relaxation reacts with the acetylating agent acetic acid and the acetylating catalyst sulfuric acid with the formation of salts; as a result, the ammonia remains - in bound form - in the acetylation and in the subsequent saponification process and finally, after the precipitation of the cellulose acetate, reaches the waste water, which is highly undesirable.

Nun ist es zwar bekannt, bei der Aktivierung von Cellulose mit flüssigem Ammoniak das Ammoniak am Ende des Prozesses mit Wasser auszuwaschen {vergleiche dazu die Zeitschrift "Faserforschung und Textiltechnik" 25 (1974), Heft 2, Seiten 57 bis 60 - Zeitschrift für Polymerforschung}, jedoch erfolgt gemäß der zuvor erwähnten Literaturstelle die Aktivierung mit dem flüssigem Ammoniak bei tiefen Temperaturen bzw. unter Kühlung, was - wie zuvor bereits in Zusammenhang mit dem in der Zeitschrift "Acta Polymerica" 32 (1981), Heft 3, Seiten 164 bis 171, beschriebenen Aktivierungsverfahren erwähnt wurde - die technische Anwendung eines solchen Aktivierungsverfahrens ziemlich aufwendig macht.Now it is known, when activating cellulose with liquid ammonia, to wash out the ammonia with water at the end of the process {see the journal "Faserforschung und Textiltechnik" 25 (1974), No. 2, pages 57 to 60 - Zeitschrift für Polymerforschung} , however, according to the previously mentioned reference, the activation takes place with the liquid ammonia at low temperatures or with cooling, which - as previously in connection with that in the magazine "Acta Polymerica" 32 (1981), No. 3, pages 164 to 171 , described activation process was mentioned - the technical application of such an activation process makes quite complex.

Der Erfindung liegt daher die Aufgabe zugrunde, ein Verfahren zur Behandlung von Cellulose, insbesondere von Zellstoff, zu deren Aktivierung für nachfolgende chemische Reaktionen, insbesondere für die nachfolgende Acetylierung, mit Hilfe von flüssigem Ammoniak zur Verfügung zu stellen, das die Vorteile der Aktivierung von Cellulose mit flüssigem Ammoniak aufweist, bei dem jedoch keine tiefen Temperaturen angewandt werden müssen, und wobei nach Abschluß der Aktivierung kein oder möglichst wenig Ammoniak in der Cellulose verbleibt. Mit der Erfindung soll auch eine hochgradige und gleichzeitig homogene Aktivierung, besonders in Hinblick auf nachfolgende Acylierungsreaktionen, erreicht werden.The invention is therefore based on the object of providing a process for the treatment of cellulose, in particular pulp, for its activation for subsequent chemical reactions, in particular for the subsequent acetylation, with the aid of liquid ammonia To provide, which has the advantages of activating cellulose with liquid ammonia, but at which no low temperatures have to be used, and wherein no or as little ammonia remains in the cellulose after completion of the activation. The invention is also intended to achieve a high-level and at the same time homogeneous activation, particularly with regard to subsequent acylation reactions.

Diese Aufgabe wird erfindungsgemäß gelöst durch ein Verfahren zur Behandlung von Cellulose zu deren Aktivierung für nachfolgende chemische Reaktionen durch Inkontaktbringen der Cellulose mit flüssigem Ammoniak bei gegenüber Atmosphärendruck erhöhtem Druck in einem Druckgefäß und anschließende Entspannung durch rasche Reduzierung des Drucks auf Atmosphärendruck, wobei

  • als Cellulose Zellstoff mit einem Gehalt an α-Cellulose von mindestens 92 Masse-% eingesetzt wird,
  • man das Ammoniak bei Raumtemperatur oder bei einer höheren Temperatur als Raumtemperatur auf den Zellstoff einwirken läßt,
  • man nach der Entspannung das im Druckgefäß dann noch verbliebene Ammoniak bis auf einen Minimalgehalt, bei dem der durch die Einwirkung des Ammoniaks erreichte Aktivierungszustand noch erhalten bleibt, entfernt
    und
  • man schließlich das für die Aufrechterhaltung des Aktivierungszustands noch notwendige restliche Ammoniak durch ein anderes Quell- oder Inklusionsmittel ersetzt.
This object is achieved according to the invention by a process for the treatment of cellulose for its activation for subsequent chemical reactions by contacting the cellulose with liquid ammonia at a pressure which is higher than atmospheric pressure in a pressure vessel and subsequent relaxation by rapidly reducing the pressure to atmospheric pressure, whereby
  • cellulose with a content of α-cellulose of at least 92% by mass is used,
  • the ammonia is allowed to act on the pulp at room temperature or at a temperature higher than room temperature,
  • after the expansion, the ammonia still remaining in the pressure vessel is removed to a minimum content at which the activation state achieved by the action of the ammonia is still retained
    and
  • finally, the remaining ammonia necessary for maintaining the activation state is replaced by another swelling or inclusion agent.

Bevorzugt wählt man als Mengenverhältnis von Ammoniak zu Zellstoff 6 Masse-Einheiten Ammoniak zu 10 Masse-Einheiten Zellstoff bis 10 Masse-Einheiten Ammoniak zu 10 Masse-Einheiten Zellstoff.Preferably, the quantitative ratio of ammonia to pulp is 6 mass units of ammonia to 10 mass units of pulp to 10 mass units of ammonia to 10 mass units of pulp.

Ferner ist es bevorzugt, daß man die Entfernung des nach der Entspannung im Druckgefäß verbliebenen Ammoniaks - bis auf dessen Minimalgehalt für die Aufrechterhaltung des Aktivierungszustands - durch Absaugen, Abpumpen, Abblasen oder durch Erwärmen des Inhalts des Druckgefäßes auf eine Temperatur, die mindestens der Raumtemperatur entspricht, bewerkstelligt.It is also preferred that the removal of the ammonia remaining in the pressure vessel after the expansion - to its minimum content for maintaining the activation state - by suction, pumping, blowing off or by heating the contents of the pressure vessel to a temperature which corresponds at least to room temperature , accomplished.

Nach einer weiteren bevorzugten Ausführungsform des erfindungsgemäßen Verfahrens beträgt der Gehalt an für die Aufrechterhaltung des Aktivierungszustands noch notwendigem restlichem Ammoniak 2 bis 4 Masse-% Ammoniak bezogen auf die Masse an Zellstoff.According to a further preferred embodiment of the method according to the invention, the content of residual ammonia still necessary for maintaining the activation state is 2 to 4% by mass of ammonia, based on the mass of pulp.

Außerdem ist es bevorzugt, daß man als anderes Quell- oder Inklusionsmittel Wasser, Wasserdampf, überhitzten Wasserdampf, einen Ether, ein Epoxid, ein Glykol, einen Kohlenwasserstoff, ein Edelgas oder Kohlendioxid einsetzt.It is also preferred that water, water vapor, superheated water vapor, an ether, an epoxy, a glycol, a hydrocarbon, an inert gas or carbon dioxide be used as another swelling or inclusion agent.

Schließlich ist es noch bevorzugt, daß das bei der Entspannung entweichende gasförmige Ammoniak aufgefangen und wieder zu flüssigem Ammoniak verdichtet wird.Finally, it is still preferred that the gaseous ammonia escaping during the expansion is collected and compressed again to liquid ammonia.

Für das erfindungsgemäße Verfahren wird ein Druckgefäß, also ein druckfestes Gefäß eingesetzt. An die Art dieses Druckgefäßes sind keine besonderen Anforderungen zu stellen. Der Begriff "Druckgefäß" soll im Sinne der Erfindung weitestgehend verstanden werden. Das Druckgefäß kann beispielsweise ein Autoklav oder für kontinuierliche Durchführung des Verfahrens ein Extruder sein. Die in der - noch nicht veröffentlichten - deutschen Patentanmeldung P 42 16 295.5 beschriebene Vorrichtung für quasi-kontinuierliche technisch-chemische Prozesse in komprimierten Fluiden läßt sich ebenfalls als Druckgefäß für das erfindungsgemäße Verfahren einsetzen.A pressure vessel, ie a pressure-resistant vessel, is used for the method according to the invention. There are no special requirements for the type of this pressure vessel. The term “pressure vessel” is to be understood as far as possible within the meaning of the invention. The pressure vessel can be, for example, an autoclave or an extruder for the process to be carried out continuously. The device for quasi-continuous technical-chemical processes in compressed fluids described in the - as yet unpublished - German patent application P 42 16 295.5 can also be used as a pressure vessel for the method according to the invention.

Gemäß der Erfindung erfolgt die Entspannung des Ammoniaks durch rasche Reduzierung des Drucks auf Atmosphärendruck Damit ist gemeint, daß die Reduzierung des Drucks auf Atmosphärendruck möglichst schlagartig erfolgen soll, vorzugsweise innerhalb eines Zeitraumes von einigen wenigen Sekunden, ganz besonders bevorzugt innerhalb eines Zeitraumes von weniger als 1 Sekunde.According to the invention, the ammonia is expanded by rapidly reducing the pressure to atmospheric pressure.This means that the pressure should be reduced to atmospheric pressure as suddenly as possible, preferably within a period of a few seconds, very particularly preferably within a period of less than 1 Second.

Zur Durchführung des erfindungsgemäßen Verfahrens wird der Zellstoff in ein Druckgefäß, wie einen Autoklaven, eingebracht und mit unter Überdruck stehendem flüssigem Ammoniak beaufschlagt. Üblicherweise ist die Temperatur im Druckgefäß dabei die Temperatur der Umgebung, also Raumtemperatur; die Anwendung höherer Temperaturen als Raumtemperatur ist jedoch auch möglich, was insofern vorteilhaft ist, als die anschließende Entfernung des Ammoniaks aus dem Druckgefäß bei der Entspannung erleichtert wird.To carry out the method according to the invention, the pulp is introduced into a pressure vessel, such as an autoclave, and liquid ammonia under pressure is applied to it. The temperature in the pressure vessel is usually the temperature of the environment, ie room temperature; however, the use of temperatures higher than room temperature is also possible, which is advantageous in that the subsequent removal of the ammonia from the pressure vessel is facilitated during the relaxation.

Mit der Erfindung werden folgende Vorteile erreicht:

  • da das erfindungsgemäße Verfahren nicht bei tiefen Temperaturen stattfindet, kann man auf aufwendige (Kühl)apparaturen verzichten.
  • mit dem erfindungsgemäßen Verfahren wird eine homogene und gleichzeitig hochgradige Aktivierung erreicht.
  • mit der Erfindung ist die Aktivierung von Zellstoff, der anschließend acetyliert werden soll, auch in großtechnischem Maßstab möglich.
The following advantages are achieved with the invention:
  • since the process according to the invention does not take place at low temperatures, expensive (cooling) equipment can be dispensed with.
  • With the method according to the invention, a homogeneous and at the same time high-level activation is achieved.
  • With the invention, the activation of pulp, which is subsequently to be acetylated, is also possible on an industrial scale.

Die Erfindung wird nachstehend anhand eines Beispiels noch näher erläutert.The invention is explained in more detail below using an example.

Beispielexample

Für das Verfahren nach der Erfindung wurde ein zylindrischer Autoklav aus V 4 A-Stahl mit einem Fassungsvermögen von 750 ml eingesetzt. In diesen Autoklaven wurden 50 g mechanisch aufgefaserter Zellstoff eingebracht. Der verwendete Zellstoff hatte einen Gehalt an α-Cellulose von 96 Masse-%.
Durch ein Ventil an der Oberseite des Autoklaven wurde 50 g flüssiges Ammoniak in den nunmehr geschlossenen Autoklaven eingeleitet, wonach das Ventil geschlossen wurde. Die Temperatur im Autoklaven betrug 20 °C. Nach Einleitung des Ammoniaks und bei der zuvor erwähnten Temperatur von 20 °C betrug der Druck im Autoklaven 6 bar. Die Dauer der Einwirkung des Ammoniaks auf den Zellstoff betrug 30 Minuten.
Nach Ablauf dieses Zeitraumes von 30 Minuten wurde das zuvor erwähnte Ventil am Autoklaven geöffnet, wodurch das Ammoniak schlagartig entwich und der Inhalt des Autoklaven auf Atmosphärendruck entspannt war.
Zur Einstellung eines Minimalgehalts an Ammoniak im Zellstoff von 4 Masse-% bezogen auf die Masse an Zellstoff wurde der Autoklav - mit geöffnetem Ventil - während eines Zeitraumes von 15 Minuten in einem Wasserbad mit einer Temperatur von 40 °C erwärmt. Der gewünschte Minimalgehalt von 4 Masse-% an Ammoniak wurde gravimetrisch überprüft.
Anschließend wurde durch das erwähnte Ventil am Autoklaven Wasserdampf in den Autoklaven eingeleitet, bis darin ein Druck von 4 bar erreicht war, wonach das Ventil wieder geschlossen wurde. Der Wasserdampf hatte dabei eine Temperatur von 145 °C. Die Dauer der Einwirkung des Wasserdampfs auf den Zellstoff betrug 5 Minuten. Danach wurde wieder auf Atmosphärendruck entspannt, indem man das mehrfach erwähnte Ventil wieder öffnete.
Anschließend wurde der Zellstoff dem Autoklaven entnommen und zur Feststellung der Reaktivität acetyliert. Dabei wurde festgestellt, daß die Acetylierungsdauer dieses Zellstoffs bis zur Cellulosetriacetat-Stufe gegenüber der eines Zellstoffs, der mit Hilfe von Eisessig aktiviert worden war, um 50 % reduziert war: Die Acetylierungsdauer für den gemäß diesem Beispiel aktivierten Zellstoff betrug lediglich 20 Minuten, wogegen die Acetylierungsdauer für einen Zellstoff, der mit Hilfe von Eisessig aktiviert worden war, 40 Minuten betrug.A cylindrical autoclave made of V 4 A steel with a capacity of 750 ml was used for the method according to the invention. 50 g of mechanically pulped pulp were placed in this autoclave brought in. The cellulose used had an α-cellulose content of 96% by mass.
50 g of liquid ammonia were introduced into the now closed autoclave through a valve at the top of the autoclave, after which the valve was closed. The temperature in the autoclave was 20 ° C. After introduction of the ammonia and at the aforementioned temperature of 20 ° C, the pressure in the autoclave was 6 bar. The duration of exposure of the ammonia to the pulp was 30 minutes.
After this period of 30 minutes, the aforementioned valve on the autoclave was opened, as a result of which the ammonia escaped suddenly and the contents of the autoclave were released to atmospheric pressure.
To set a minimum ammonia content in the pulp of 4% by mass, based on the mass of pulp, the autoclave - with the valve open - was heated in a water bath at a temperature of 40 ° C. for a period of 15 minutes. The desired minimum ammonia content of 4% by mass was checked gravimetrically.
Subsequently, steam was introduced into the autoclave through the aforementioned valve on the autoclave until a pressure of 4 bar was reached, after which the valve was closed again. The water vapor had a temperature of 145 ° C. The duration of exposure to water vapor to the pulp was 5 minutes. The pressure was then released again to atmospheric pressure by opening the valve mentioned several times.
The pulp was then removed from the autoclave and acetylated to determine the reactivity. It was found that the acetylation period of this pulp up to the cellulose triacetate stage was reduced by 50% compared to that of a pulp which had been activated with glacial acetic acid: the acetylation period for the cellulose activated according to this example was only 20 minutes, whereas that Acetylation time for a pulp that was activated with glacial acetic acid was 40 minutes.

Ferner wurde festgestellt, daß die Reaktionslösung aus nach diesem Beispiel acetyliertem Zellstoff (= Cellulosetriacetat-Lösung) sehr homogen und frei von Zellstoffasern war.It was also found that the reaction solution of cellulose acetylated according to this example (= cellulose triacetate solution) was very homogeneous and free of cellulose fibers.

Claims (6)

Verfahren zur Behandlung von Cellulose zu deren Aktivierung für nachfolgende chemische Reaktionen durch Inkontaktbringen der Cellulose mit flüssigem Ammoniak bei gegenüber Atmosphärendruck erhöhtem Druck in einem Druckgefäß und anschließende Entspannung durch rasche Reduzierung des Drucks auf Atmosphärendruck, wobei - als Cellulose Zellstoff mit einem Gehalt an α-Cellulose von mindestens 92 Masse-% eingesetzt wird, - man das Ammoniak bei Raumtemperatur oder bei einer höheren Temperatur als Raumtemperatur auf den Zellstoff einwirken läßt, - man nach der Entspannung das im Druckgefäß dann noch verbliebene Ammoniak bis auf einen Minimalgehalt, bei dem der durch die Einwirkung des Ammoniaks erreichte Aktivierungszustand noch erhalten bleibt, entfernt
und - man schließlich das für die Aufrechterhaltung des Aktivierungszustands noch notwendige restliche Ammoniak durch ein anderes Quell- oder Inklusionsmittel ersetzt. Process for the treatment of cellulose for its activation for subsequent chemical reactions by contacting the cellulose with liquid ammonia at a pressure which is higher than atmospheric pressure in a pressure vessel and subsequent relaxation by rapidly reducing the pressure to atmospheric pressure, whereby cellulose with a content of α-cellulose of at least 92% by mass is used, the ammonia is allowed to act on the pulp at room temperature or at a temperature higher than room temperature, - After the expansion, the ammonia still remaining in the pressure vessel is removed to a minimum content at which the activation state achieved by the action of the ammonia is still retained
and - Finally, the remaining ammonia necessary for maintaining the activation state is replaced by another swelling or inclusion agent. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man als Mengenverhältnis von Ammoniak zu Zellstoff 6 Masse-Einheiten Ammoniak zu 10 Masse-Einheiten Zellstoff bis 10 Masse-Einheiten Ammoniak zu 10 Masse-Einheiten Zellstoff wählt.A method according to claim 1, characterized in that the quantitative ratio of ammonia to pulp 6 mass units Choose ammonia to 10 mass units of pulp to 10 mass units of ammonia to 10 mass units of pulp. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß man die Entfernung des nach der Entspannung im Druckgefäß verbliebenen Ammoniaks - bis auf dessen Minimalgehalt für die Aufrechterhaltung des Aktivierungszustands - durch Absaugen, Abpumpen, Abblasen oder durch Erwärmen des Inhalts des Druckgefäßes auf eine Temperatur, die mindestens der Raumtemperatur entspricht, bewerkstelligt.A method according to claim 1 or 2, characterized in that the removal of the ammonia remaining in the pressure vessel after the expansion - apart from its minimum content for maintaining the activation state - by suction, pumping, blowing off or by heating the contents of the pressure vessel to a temperature, which corresponds at least to the room temperature. Verfahren nach mindestens einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß der Gehalt an für die Aufrechterhaltung des Aktivierungszustands noch notwendigem restlichem Ammoniak 2 bis 4 Masse-% Ammoniak bezogen auf die Masse an Zellstoff beträgt.Method according to at least one of Claims 1 to 3, characterized in that the content of residual ammonia which is still necessary for maintaining the activation state is 2 to 4% by mass of ammonia, based on the mass of pulp. Verfahren nach mindestens einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß man als anderes Quell- oder Inklusionsmittel Wasser, Wasserdampf, überhitzten Wasserdampf, einen Ether, ein Epoxid, ein Glykol, einen Kohlenwasserstoff, ein Edelgas oder Kohlendioxid einsetzt.Process according to at least one of Claims 1 to 4, characterized in that water, water vapor, superheated steam, an ether, an epoxide, a glycol, a hydrocarbon, a noble gas or carbon dioxide are used as the other swelling or inclusion agent. Verfahren nach mindestens einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß das bei der Entspannung entweichende gasförmige Ammoniak aufgefangen und wieder zu flüssigem Ammoniak verdichtet wird.Process according to at least one of Claims 1 to 5, characterized in that the gaseous ammonia escaping during the expansion is collected and compressed again to form liquid ammonia.
EP94111025A 1993-09-04 1994-07-15 Process for treating cellulose Expired - Lifetime EP0641802B1 (en)

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